1. Field of the Invention
The present invention relates to a focus adjusting apparatus for an image pickup apparatus, for example, a television camera.
2. Description of the Related Art
In a focus adjusting apparatus for an image pickup apparatus, for example, a television camera, focus adjustment is performed by a servo unit including a driving system (for example, motor) and a control system for controlling the driving system. In order to supply a commanding signal to the control system of the servo unit, a focus demand 18 as illustrated in FIG. 15 is used.
FIG. 16 is a block diagram illustrating a conventional focus adjusting apparatus for a television lens. An operating amount of the focus demand 18 is first detected. Then, a focus command signal from a zoom-focus operating circuit 17 which computes a focus command value and a focus position signal from a focus position detecting unit 10 are input to a lens controller 9. The lens controller 9 outputs, to a focus driver 13, a focus controlling signal for adjusting a difference between the focus command signal and the focus position signal to 0. Next, the focus driver 13 controls a focus motor 14 in response to the focus controlling signal to control a focus lens. In this case, the operating amount of the focus demand 18 and a driving amount of the focus lens have a linear relationship as illustrated in FIG. 17.
When the operating amount of the focus operating knob (focus demand) and the driving amount of the focus lens have the linear relationship, focusing sensitivity relative to the rotation amount (operating amount) of the focus operating knob increases under a condition in which an field depth is small. Therefore, there has been proposed a focus adjusting apparatus in which the focus driving amount relative to the operating amount of the focus operating knob is determined based on the field depth information (for example, Japanese Patent No. 3429050 or Japanese Patent Application Laid-Open No. 3-36511).
However, when the focus driving amount relative to the operating amount of the focus operating knob is determined based on the depth information, the following problem arises. For example, when the field depth is small, focusing in the vicinity of an in-focus position is easy. However, in a case where a focus deviation amount is large, a focal position cannot reach the in-focus position unless the operating amount of the focus operating knob is increased.